Hi @acgrieve32 ,

You would need to completely dis-assemble the XBox and use IPA 99%+ to clean away all the traces of moisture and corrosion. (IPA - Isopropyl Alcohol - available at electronics parts stores. Try not to use 'rubbing alcohol' as this is sometimes <70% IPA , can sometimes contain additives and is not as effective. Check the label if you do decide to use it.

Here is a link to the ifixit Xbox One S repair guides which should be of some help.

Here is a link that in general describes what to do to try and recover a device which has had water damage.

Electronics Water Damage

Hopefully this is of some help